1. Field of the Invention
The present application relates to powertrains for hybrid-electric, all-wheel drive vehicles and to a method for managing power distribution to vehicle traction wheels.
2. Background Art
U.S. patent application Ser. No. 10/463,046, filed Jun. 17, 2003, identified above, and U.S. Pat. No. 5,856,709 disclose hybrid-electric powertrains capable of delivering driving torque to traction wheels of an automotive vehicle through a geared transmission that establishes multiple powerflow paths from an engine power source and an electrical power source. The '046 patent application is assigned to the assignee of the present invention.
The powertrains disclosed in the '709 patent, as well as the copending '046 patent application, may be adapted to both front-wheel drive and rear-wheel drive configurations for hybrid-electric vehicles. U.S. Pat. No. 6,176,808 discloses another example of a hybrid-electric vehicle powertrain of this type.
The '046 patent application and the '808 and '709 patents are incorporated in the disclosure of this application by reference.
In known geared transmission configurations for hybrid-electric vehicles with multiple power sources, an electric motor typically is connected to the driving wheels through a set of fixed ratio gears. This provides improved launch torque as motor torque is multiplied by the gearing. A high torque multiplication for the torque flow path for the motor, however, requires a compromise between the maximum output speed required and the initial acceleration torque needed during a vehicle launch if the electric motor gearing has a fixed ratio. The need for this is due in part to the use of fixed ratio gearing in the driving torque flow paths from the multiple power sources to the traction wheels.
In the case of a hybrid-electric vehicle powertrain of the kind disclosed in the previously identified copending patent application, recovery of regenerative electrical energy in the powertrain may be limited because the electric motor is connected mechanically only to the rear traction wheels.